Medical robotic systems such as those used in performing minimally invasive surgical procedures offer many benefits over traditional open surgery techniques, including less pain, shorter hospital stays, quicker return to normal activities, minimal scarring, reduced recovery time, and less injury to tissue. Consequently, demand for minimally invasive surgery using such medical robotic systems is strong and growing.
Examples of medical robotic systems include the da Vinci® Surgical System and the da Vinci® S™ Surgical System from Intuitive Surgical, Inc., of Sunnyvale, Calif. Each of these systems includes a surgeon's console, a patient-side cart, a high performance three-dimensional (“3-D”) vision system, and Intuitive Surgical's proprietary EndoWrist® articulating instruments, which are modeled after the human wrist so that when added to the motions of manipulators holding the surgical instruments, they allow at least six degrees of freedom of motion, which is comparable to or even greater than the natural motions of open surgery.
The da Vinci® surgeon's console has a high-resolution stereoscopic video display with two progressive scan cathode ray tubes (“CRTs”). The system offers higher fidelity than polarization, shutter eyeglass, or other techniques. Each eye views a separate CRT presenting the left or right eye perspective, through an objective lens and a series of mirrors. The surgeon sits comfortably and looks into this display throughout surgery, making it an ideal place for the surgeon to display and manipulate 3-D intraoperative imagery.
The patient-side cart typically includes three or more robotic arm assemblies with corresponding slave manipulators for holding and manipulating medical devices such as surgical instruments and image capturing devices for performing and/or viewing a medical procedure at a surgical site within a patient. To manipulate these medical devices, the surgeon's console also includes input devices which may be selectively associated with the medical devices and their respective slave manipulators. Since the movements of the input devices and their associated medical devices are scaled, this allows the surgeon to perform intricate medical procedures with greater ease than conventional open surgery. Further, it may even allow the surgeon to perform medical procedures that are not even feasible using conventional open surgery techniques.
To perform a minimally invasive surgical procedure on a patient, one or more incisions are first made in the patient and cannulae inserted therein to gain access to a surgical site within the patient. Setup arms supporting the slave manipulators are then positioned so as to allow the slave manipulators to attach to respective of the cannulae. Surgical instruments engaged on the slave manipulators are then inserted into the cannulae and properly positioned and oriented in order to perform the procedure. A surgeon may then manipulate input devices which are coupled to the slave manipulators and their respective surgical instruments through one or more controllers to perform the medical procedure.
Although minimally invasive surgery enables keyhole access to many surgical sites while avoiding the loss of dexterity associated with earlier laparoscopic techniques, it still has the drawback compared to open surgery of reducing the surgeon's feeling of touch and of contact forces. During the performance of a medical procedure, however, it may be desirable to prevent a surgical instrument's end effector from exerting excessive force.
As an example, if the end effector is a gripper being used for suturing, a surgeon may need to tie a knot as hard as possible short of breaking the suture. This may be difficult to do if the surgeon cannot feel how much force he or she is applying against the suture. Thus, it would be desirable in such case to not only provide some mechanism to prevent the surgeon from inadvertently breaking the suture, but also to give the surgeon some warning when the applied force is getting too strong for the current application.
As another example, if the end effector is an atraumatic grasper used to retract tissue or an organ, a surgeon may need to provide sufficient retraction to clear the operating field while avoiding to pull too hard on the tissues and blood supply to the retracted organ. Thus, it would be desirable in such case to again provide some mechanism to prevent the surgeon from inadvertently damaging the tissue or organ being retracted.
Many approaches, going under the general name of force feedback systems, have been proposed in the scientific literature to reproduce on the input control devices the same forces experienced by the instrument end effectors. Unfortunately in practice such approaches all suffer from the general shortcoming of low fidelity and delayed reproduction of the slave force on the input devices. Moreover force feedback systems in the literature always offer some risk of producing uncontrolled motions such as system instabilities, depending on the properties of the contact at the end effector and input device sides, and therefore, may not be generally suited for medical applications.